How Frequently Do Cottonmouths (Agkistrodon piscivorus) Bask in Trees?

Abstract

A common belief in the southeastern United States is that Cottonmouths (Agkistrodon piscivorus) bask frequently in tree branches over the water's edge and are therefore of considerable hazard for anglers and boaters. Although this notion is almost certainly based upon observations of nonvenomous watersnakes (Nerodia spp.), there are no quantitative data that specifically address this belief. I analyzed a 7-yr dataset on Cottonmouths from two populations (Georgia and Alabama) to determine the frequency of this behavior by Cottonmouths. I recorded behavioral and substrate information for 804 separate observations on Cottonmouths. Only two of these Cottonmouths were exhibiting arboreal behavior (0.25% of observations)—snakes observed over the ground or water surface on branches narrower than their own bodies—confirming that this is indeed a very rare tendency in this species and not likely to be observed by the public. Instead, I frequently encountered Cottonmouths on the ground along the water's edge in their characteristic ambush posture, uncoiled in aquatic situations, or coiled on elevated platforms (e.g., hummocks, piles of driftwood, logs, beaver lodges). This demonstrates that Cottonmouths have the capacity to climb but are not likely to be observed in arboreal situations. Few snakes in North America are as easily observed, frequently encountered, and misunderstood by the public as Cottonmouths (Agkistrodon piscivorus). Previous research has demonstrated that anecdotal accounts of aggressive behavior in this species—widely believed by the general public throughout the range of this snake—are unfounded (Gibbons and Dorcas, 2002; Glaudas, 2004; but see Means, 2010). Although factual information is becoming available through television and internet media, additional research is necessary to dispel myths regarding this and other snake species. Another widespread belief common in the Southeast is that Cottonmouths bask in the branches of trees and shrubs at the water's edge and often fall on hapless boaters. This belief has been articulated to J. W. Gibbons (Savannah River Ecology Laboratory, pers. comm.), J. B. Jensen (Georgia Department of Natural Resources, pers. comm.), C. Guyer (Auburn University, pers. comm.), and myself (pers. obs.). Although this belief is most likely a myth based upon encounters or stories involving misidentified watersnakes, there are currently no published data that refute the assertion that Cottonmouths bask in trees. Moreover, while several reviews of Cottonmouth natural history suggest that this species is generally found at the water's edge, floating on water, or lying on terrestrial substrates (Gloyd and Conant, 1990; Campbell and Lamar, 2004; Ernst and Ernst, 2004; Gibbons and Dorcas, 2005), these sources also mention that Cottonmouths are occasionally observed in trees and shrubs near the water's edge. These assertions are based largely on anecdotal observations and could be misinterpreted by lay readers who frequently misidentify watersnakes (Nerodia spp.) as Cottonmouths (Gibbons and Dorcas, 2004), which frequently bask from such perches (Tiebout and Cary, 1987; Gibbons and Dorcas, 2004). To date, no quantitative comparison of arboreal versus terrestrial (or aquatic) tendencies in the Cottonmouth is available. Reports of other terrestrial pit vipers exhibiting surprisingly arboreal feats (e.g., Timber Rattlesnake, Crotalus horridus; Coupe, 2001, Rudolph et al., 2004) further indicate the need for accurate information about Cottonmouths. To determine the frequency that observers might expect to find Cottonmouths basking above the water surface in vegetation, I analyzed my own observations of 804 encounters with Cottonmouths during 2003-09 from sites in Georgia and Alabama. I analyzed the frequency with which I found Cottonmouths in arboreal, aquatic, or elevated substrates and the behaviors they were exhibiting from these positions.